Mythic HFC drops 720 gear. Your raid was mostly 740+ before you ever got an orange ranking. When you were actually progressing, you mostly ranked in the 40s with several sub-20s. What you did is called getting carried.
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The point was just that different tanks require different strategies due to their weakness making difficulty vary by tank and comp for each boss, but prot pally fanboys seem to think they can heal as good as a DK and mitigate as good as a warrior so you can simply face tank everything at any difficultly level.